Everything that has a temperature gives off electromagnetic radiation (light). The sun is extremely hot and has a lot of energy to give, so it gives off shortwave radiation because shortwave radiation contains higher amounts of energy The earth is much cooler, but still emits radiation. Earth’s radiation is emitted as longwave because longwave radiation contains a smaller amount of energy.
Why Do I Care? Shortwave and longwave radiation interact with the earth and atmosphere in different ways.
Shortwave radiation (visible light) contains a lot of energy; longwave radiation (infrared light) contains less energy than shortwave radiation (shortwave radiation has a shorter wavelength than longwave radation). Solar energy enters our atmosphere as shortwave radiation in the form of ultraviolet (UV) rays (the ones that give us sunburn) and visible light. The sun emits shortwave radiation because it is extremely hot and has a lot of energy to give off. Once in the Earth’s atmosphere, clouds and the surface absorb the solar energy. The ground heats up and re-emits energy as longwave radiation in the form of infrared rays. Earth emits longwave radiation because Earth is cooler than the sun and has less energy available to give off.
Figure A shows the Atmospheric Window of the wavelengths that enter our atmosphere. Our atmosphere is transparent to radio waves, visible light, and some infrared and UV radiation.
How does this relate to public health?
Exposure to ultraviolet (UV) rays from the sun (shortwave radiation) is said to cause 65% to 90% of melanoma of the skin, which accounts for three-fourths of all skin cancer deaths.1,2 Additionally, the sun’s UV rays can also cause cataracts and other damage to the eye.3 On the other hand, exposure to UV rays impacts vitamin D circulation, which is said to be a protective factor against colon and rectum cancer.4
1Centers for Disease Control and Prevention. Basic information about skin cancer. April 24, 2012. <http://www.cdc.gov/cancer/skin/basic_info/> Accessed November 17, 2012.
2National Cancer Institute. Skin cancer. (n.d.) <http://www.cancer.gov/cancertopics/types/skin> Accessed January 27, 2012.
3World Health Organization. Ultraviolet radiation and human health. December 2009. <http://www.who.int/mediacentre/factsheets/fs305/en/index.html> Accessed November 17, 2012.
4 Portier CJ, et al. 2010. A human health perspective on climate change: a report outlining the research needs on the human health effects of climate change. Research Triangle Park, NC: Environmental Health Perspectives/National Institute of Environmental Health Sciences. doi:10.1289/ehp.1002272 <www.niehs.nih.gov/climatereport> Accessed November 17, 2012.
Want to learn more?Earth's Energy Balance, Albedo
Activities to accompany the information above:
Activity: What is a Greenhouse? (Link to original activity.)
Description: This activity focuses on how a greenhouse retains heat. Students will build a greenhouse model to explain this process.